8.3 Phases and Phase Changes

2. 8.3 Phases and Phase Changes Matter Video http://preparatorychemistry.com/KMT_flash.htm

3. The Phases of Matter • A solid holds its shape and does not flow. • The molecules in a solid vibrate in place.

4. The Phases of Matter • A liquid holds its volume, but does not hold its shape—it flows. • Liquids flow because the molecules can move around.

5. The Phases of Matter • A gas flows like a liquid, but can also expand or contract to fill a container. • A gas does not hold its own volume or shape. • The molecules in a gas have enough energy to completely break away from each other.

6. Intermolecular Forces When molecules are close together, they are attracted through intermolecular forces. The forces in chemical bonds are stronger than intermolecular forces.

7. Intermolecular Forces Most attractive in solids Each phase change uses energy Energy overcomes intermolecular forces

8. liquid solid Phase Changes liquid solid gas liquid liquid gas solid gas gas solid

9. Plasma In the plasma phase, matter becomes ionized as electrons are broken loose from atoms. The Sun is made of plasma, as is most of the universe

10. 8.3 Melting and boiling • The melting point is the temperature at which a substance changes from a solid to a liquid.

11. Heating and Cooling Curves Why is the temperature constant during a phase change? Freezing Heat energy is being used to break intermolecular forces

12. 8.3 Melting and boiling • The temperature at which a liquid becomes a gas is called the boiling point.

13. 8.3 Melting and boiling points ofcommon substances • Materials have a wide range of melting and boiling points.

15. Heating and Cooling Curves Temperature ( oC ) Time (s)

16. Exit Question • Explain why heating/cooling curves are flat during phase changes.